Shea McClellin (99) brings down Aaron Rodgers. / Jeffrey Phelps, AP

by Weston Hodkiewicz, USA TODAY Sports

by Weston Hodkiewicz, USA TODAY Sports

GREEN BAY, Wis. - Green Bay Packers quarterback Aaron Rodgers suffered a left shoulder injury following the first series of Monday night's game against the Chicago Bears and did not return.

Rodgers appeared to injure his shoulder on a Shea McClellin sack with 12:38 remaining in the first half. He completed one pass for 27 yards to Jordy Nelson before exiting.

Rodgers was briefly examined by team doctor Patrick McKenzie before jogging off to the locker room. He returned to the sideline in the third quarter in sweats and no sling on his shoulder.

"He has a shoulder injury," Packers coach Mike McCarthy said. "They want to run more tests. They don't have an exact diagnosis. We'll have more information, probably tomorrow."

Pressed for more information, McCarthy insisted there wasn't any.

"No timeline, no exact diagnosis," he said. "That's where we're at."

Without Rodgers, the Packers turned to veteran backup quarterback Seneca Wallace, who was serviceable managing the offense in his first regular-season snaps since quarterbacking Cleveland in a 13-9 loss to Pittsburgh on Jan. 1, 2012.

Wallace's night didn't get off to a good start. On his first series, Bears defensive end Julius Peppers popped a pass up at the line of scrimmage and picked it off.

"Aaron's a huge part of our offense," McCarthy said. "This is a thing that's been built over time with Aaron as the centerpiece. I don't think it's realistic to put anyone in there and expect him to perform (like Rodgers)."

Running back James Starks rushed for a 32-yard touchdown on the first play of Wallace's second series, but the offense finished the first half going three-and-out twice and never crossed the Bears' 40-yard line.

Wallace is the only backup quarterback currently on the active roster, though third-year pro Scott Tolzien recently received a significant salary boost to remain on the practice squad after receiving overtures from the Browns.

Coincidentally, Matt Flynn, who served as Rodgers' backup from 2008-11, was released by Buffalo on Monday.